1. Field of the Invention
The present invention relates to a DC power supply device for an electronic device and, particularly to a technology for sharing to supply power from a battery according to a power interruption of AC input or a loading state.
2. Description of Prior Art
Conventionally, a power supply for an information device such as a disk array is constituted such that power is supplied from a commercial AC input, an AC/DC converter converts the input into DC power, and a DC/DC converter converts the DC power to a DC voltage required for a load inside the information device again. In this type of inboard power supply, the AC/DC converters and the DC/DC converters operate redundantly in parallel for increasing reliability.
Also a power supply constitution where an uninterruptible power supply (UPS) is attached externally or a constitution where an input of the AC/DC converter receives two systems of AC are adopted.
Japanese Laid-open Patent Application No. 2000-116029 JP A 2000-116029) (Japanese Patent Application No. 10-280829) discloses a backup power supply device supplying power from a battery when AC power supply is interrupted. The power supply constitution adopts a circuit constitution where a diode is serially connected to a power factor improving circuit conducting AC/DC conversion, and a diode is serially connected to a backup converter from a battery, and then both of the diodes are connected in parallel. Output voltage from the backup converter is set to lower than output voltage of the power factor improving circuit, and either the power factor improving circuit or the backup circuit supplies power to a load, thereby integrating a UPS feature into a device power supply, resulting in improving reliability of the power supply device in case of a trouble of the AC power supply.
Problem to be Solved by the Invention
The conventional power supply constitution where an external UPS is connected degrades the conversion efficiency because there are two stages of power conversion in the UPS during normal operation, and further there is an AC/DC converter for converting AC power to DC power in a communication/information device, resulting in requiring three stages of power conversion. Also the converters providing redundant features are constituted by connecting them in multiple stages, there is a problem that the volume of the power supply device becomes large, and the cost increases.
As communication/information devices have diversified, a power supply is required to meet a wide range of input, since a user selects a device without caring the input voltage. However, if an external UPS is connected, the input/output specification is fixed, and there is a problem that a power supply whose input voltage specification meets a user environment should be selected.
Though the power supply constitution in the Japanese application patent laid-open publication described before allows reducing the size and the cost compared with the one provided with an external UPS, the maximum power required for the DC/DC converter is supplied from the backup converter when the AC power supply has a trouble, and from the power factor improving circuit which conducts AC/DC conversion when in a normal state. Thus, both the backup converter and the power factor improving circuit should have a capability supplying the maximum power which a load requires, resulting in problems of increased volume, size and cost of the device.
An object of the present invention is to provide a DC power supply device which improves power conversion efficiency as the entire power supply device, saves space, reduces the cost, and does not present a power interruption or a momentary power failure.
To attain the object as mentioned above, a DC power supply device comprising, an AC/DC converter which converts a commercial AC input to DC voltage, a DC/DC converter which converts output power of the AC/DC converter into load voltage, and a DC converter converting DC power from a battery to DC voltage corresponding to the output of the AC/DC converter to connect to output terminals of the AC/DC converter is provided, and the DC power supply device is provided with a control circuit which controls the output voltage of the AC/DC converter and the output voltage of the DC converter to prescribed values, the AC/DC converter and the DC converter supply power in parallel when a load is more than a prescribed value, and the DC converter supplies power as a backup when a trouble is present in the AC power input.
The control circuit is provided with a voltage control circuit which controls the output voltage of the AC/DC converter to a prescribed value, a current command circuit which forms a current command for the AC/DC converter, a PFC controlling part which controls the AC/DC converter, a UPS controlling part which controls the DC converter to conduct a prescribed operation, a voltage level detecting circuit, and a current calculating circuit, and controls the current command circuit, the PFC controlling part, and the UPS controlling part according to outputs from the voltage level detecting circuit and the current calculating circuit, thereby operating the AC/DC converter and the DC converter. The control circuit is further provided with an AC power interruption detecting circuit, and the AC power interruption detecting circuit simultaneously uses a power interruption detection in the AC input, and a power interruption detection by comparing the current command from the AC/DC converter and an actual detected current, and impresses a power interruption signal on the voltage level detecting circuit when a power interruption is detected.